Dual input clutch transmissions have been designed with friction launch clutches to connect a vehicle engine to selectively engaged gears in a lay shaft transmission. Dual input clutch transmissions are designed to permit engine power to be distributed through power paths that are dependent upon which input clutch is engaged. Dual input clutch power transmissions are typically designed as countershaft-type transmissions (i.e., lay shaft transmissions) wherein engagement of a first of the input clutches creates a power path from an input shaft through a first countershaft to an output shaft, and engagement of a second of the input clutches creates a power path through a second countershaft to the output shaft. Synchronizers engage gears with the countershafts to complete the powerflow to the output shaft. Layshaft designs and other transmission configurations that use synchronizers for selectively engaging gears with a shaft provide relatively low spin losses, thus enhancing overall operating efficiency.
The art has also employed the clutch of a planetary transmission as a friction launch mechanism that provides launch slip in connecting a set of interconnected planetary gear sets with an input shaft connected to an engine to transfer power from the input shaft to an output shaft. One such power transmission with a friction launch torque-transmitting mechanism is disclosed in commonly-assigned U.S. Pat. No. 6,471,616, issued to Paul D. Stevenson on Oct. 29, 2002, which is hereby incorporated by reference in its entirety.
Furthermore, the art has also employed a torque converter connectable with planetary or layshaft gear sets in a transmission to transfer power from a power source, such as an engine, to an output shaft. The torque converter provides a torque multiplier and speed differential between the engine and the gearing. The fluid coupling function of the torque converter enables a smooth transmission of power during launch, shifting, as well as coasting. A torque converter clutch may or may not be employed to connect the engine to the transmission (bypassing the torque converter) and thereby improve the overall efficiency of the transmission. An example of a powertrain including an engine, a torque converter and a transmission including three planetary gear sets is described in commonly-assigned U.S. Pat. No. 6,729,993, issued to Norman Kenneth Bucknor et al. on May 4, 2004, which is hereby incorporated by reference in its entirety.